1. Field of the Invention
The present invention relates to a piezoelectric actuator, a probe-driving mechanism, methods of production thereof, and an apparatus employing the same such as a tunnel current-detecting device and an information-processing device.
2. Related Background Art
In recent years, application of STM technique is investigated in a variety of technical fields including observation and evaluation of semiconductors and high-molecular materials in atomic or molecular order, fine working, and recording apparatus.
In particular, recording apparatuses are required to have large capacity in calculation information and image information of a computor, and so forth, and development of STM technique therefor is more and more strongly demanded. As the result of progress in semiconductor processing technique, microprocessors have come to be miniaturized and computing ability has been improved. Consequently, recording apparatuses are desired to be further miniaturized. To satisfy such requirements, a recording-reproduction apparatus is disclosed which employs a transducer having a tunnel-current-generating probe provided on a driving means capable of fine adjustment of the gap between the probe and a recording medium. This apparatus records information by applying voltage with the transducer to change the work function on the surface of the recording medium, or reads out information by detecting the change of a tunnel current caused by the change of the work function, at the minimum recording area of 10 nm square (Japanese Patent Application Laid-Open No. 63-161552).
Generally, the probes need to be increased in number in order to accelerate transfer and recording of data. In the transfer or recording of data in the aforementioned apparatus, the probes run along the lines of recorded data by adjusting the space between the probe and a recording medium. Since the breadth of the lines of the recorded data is extremely small, stable recording-reproduction cannot readily be achieved owing to the drift caused by the temperature variation of the apparatus, run-out of the probes from the data lines caused by external vibration, and other influences. Accordingly, the respective probes are required to move independently in high speed in a direction perpendicular to the face of the recording medium.
To satisfy such requirement, W089/07256, for example, discloses a cantilever constituted of lamination of piezoelectric material layers 5, 7 and electrode layers 4, 6, 8 as shown in FIG. 6. The cantilever is prepared by forming an insulating layer 11 composed of silicon oxide film, patterning it, and etching anisotropically a substrate 1 to have a bimorph arm 10.
In the above example of the prior art, however, the thickness of the insulating layer 11 needs to be made thin to suppress side-etching of the Si substrate 1 in the etching of the bimorph arm 10 and the insulating layer 11. Thereby, nonnegligible capacitance is induced between the lower electrode 4 and the Si substrate 1, forming an equivalent circuit by connection with another electrode through the substrate as shown in FIG. 7.
Usually, the driving frequency of a cantilever is limited by the resonance frequency determined by the dimension and the layer constitution of the cantilever. In the example of the above prior art, the driving frequency is limited also by the increase of the time constant caused by the capacitance induced by the piezoelectric substance layers 5, 7 and the aforementioned parasitic capacitance. Consequently, the adjustment of the spacing between a medium and the probe becomes impossible and malfunction arises in writing and reading. In a multi-probe construction, difference in lengths of wiring to the driving electrodes for respective probes causes large variation of the parasitic capacitance, which causes variation of the driving characteristics of the cantilever.
If the insulating layer under the electrode is made thick to reduce the parasitic capacity for the purpose of avoiding the above problems, Si is isotropically etched, when the insulating layer 11 is etched, in the side direction in a dimension of ten times larger or more than the thickness of the insulating layer as shown in FIG. 6, which lowers the controllability of the cantilever.